Equalizing system



Jan. 10, 1939. A, H. BUCKLEY 2,142,994

' EQUALIZING SYSTEM Filed April 16, 1935 PLATE CURRENT B IE. 5 4 a a lo w n a i: .l 0 'l NssnrwsGmn PoreNTnm. I Nssnnve Gmo Porermm.

I l l I i 5l Patented Jan. 10, 1939 UNITED STATES PATENT OFFICE EQUALIZING SYSTEM Application April 16, 1935, Serial No. 16,657

16 Claims.

My invention relates in general to electrical translation and has more particular reference to a transfer system for electrical Waves or impulses wherein it is desired to reduce all impulses supplied to the system to a predetermined value of signal strength.

An important object of the invention is to provide a signal equalizer system adapted to reduce impulses of all frequencies impressed on the system, including interference and other undesired impulses, to a common strength so that the desired signal may be separated and identified from the others Without difficulty whereby signal frequency selective circuits may be utilized at maximum efficiency in communication systems.

Another object of the invention is to provide, for use in a code communication circuit, a circuit effectively suppressing impulses of frequencies other than the desired frequency, even though the interfering impulses greatly eX- ceed in amplitude the impulses of the desired frequency.

Another important object is to provide a transfer system for supplying to a load device operating voltage impulses of an amplitude which is constant and substantially independent of the amplitude of the impulses supplied to the transfer system.

A further important object of the invention is to provide in a radio receiver for telegraph signals, or the like, means to reduce all impulses to a common and unvarying amplitude and to select from the impulses of common amplitude signal impulses of the desired frequency, whereby all interfering impulses of Whatever amplitude and whatever frequency may be effectively eliminated.

Another important object of the invention is to provide a relay operating circuit, or the like, wherein all voltage impulses supplied to the input of the circuit are reduced to a common, constant amplitude, filtered and the impulses of the desired frequency supplied to the relay, or to the load device, whereby false operation of the relay by strong impulses of interfering frequencies is prevented.

Another object is to provide means to avoid the deleterious effects of amplification of interfering impulses while amplifying a desired signal, in order to eliminate the detrimental effect of fading.

Another important object of the invention is to provide, for use in connection with a device which is extremely critical as to operating potential, such as a Thyratron tube, a transfer system of such character that it impresses upon the device operating impulses having a maximum potential amplitude which is constant and substantially independent of the amplitude of the impulses received by, or supplied to, the system, to thereby prevent false operation of the relay.

Another important object resides in providing a new method of controlling signal translation by reducing all impulses to a common strength factor or amplitude in order to thus preserve a desired signal against the effects of otherwise uncontrollable interference.

Referring to the drawing:

Figure l is a circuit diagram illustrating a signal equalizer embodying my invention; and

Figure 2 is a graph illustrating ideal grid Voltage-plate current curves for two electronic devices forming a part of the apparatus shown in Figure l.

To illustrate my invention, I have shown on the drawinfr a signal equaliter system 9 having an input I i, at which impulses may be impressed upon the system. It will be understood, of course, that the equalizer system is adapted for use wherever it may be desired to translate electrical irnpulses and waves and, while it is particularly adapted for use more especially in radio transmission and` reception of signal impulses, the system has application where it is desired to equalize electrical impulses fo1` any purpose whatever. t will be further understood that the impulses treated may be utilized in the performance of, or control of, any useful function at the receiving point to which the same are or may be transferred. Any suitable means or electrical network may be utilized for supplying electrical impulses to the input of the system. Where the device is used in a radio telegraph receiver, for example, the input is or may be connected to a suitable receiving antenna either directly or through additional signal translating systems.

From the input, the impressed impulses are conducted through parallel circuits, in each of which there is an electronic tube, preferably of the three-element thermionic type, the grids of which are maintained at different xed bias potentials. The plates or anodes of the electronic tubes are connected together in opposition through the primary winding of a suitable transformer, so that the transformer is energized by the differential of impulses passed by the electronic tubes in the parallel circuits aforesaid.

The system contemplates that all input impulses will be applied equally to both of the parallel circuits and transferred thence unequally to the output transformer. The unequal impulses are subtracted, but the difference of their maximum amplitude is maintained constant by suitable independent adjustment of the grid bias potential of each tube. The frequencies of the applied impulses, however, will be reproduced in the system in a radio telegraph receiver, wherein received impulses are applied to the performance of any desired function, as, for example, the operation of a relay, which, in turn, may be connected to operate or control any device, such as a typewriter, at the receiving station. In such an arrangement, it is possible to cause'the control relay to operate in response to a signal impulse of predetermined strength and frequency. In the transmission of signal impulses, particularly by radio, the character of the wave may be considerably changed by superimposed interference, whereby the wave becomes distorted without change in frequency. Fading, a well known phenomenon inradio transmission, is another cause which results in changing the strength Vcharacter of a carrier wave.

My signal equalizing system, however, functions to receive a wave, no matter how much itis distorted in transmission and transfer the same to the output circuit at a desired uniform strength. Incidentally, where the device is used for radio1 reception, the input, being connected to the receiving antenna, may receive much interference along with the desired wave of operating or signalling frequency. This interference may be in the form of waves transmitted from interfering stations, or may be the result of electrical atmospheric disturbance. Such interference. whatever its nature, in passing through the equalizing system, is reduced tc the same strength as the transferred signal impulse and may be differentiated and separated without diificulty by suitable filtering means in or connected to the output of the equalizer system.

For the purpose of illustrating the invention, I have shown, in Figure 1 of the drawing, a preferred arrangement, in which the input comprises a transformer 2|, one winding of which provides the input connection and the other winding of which is connected with the cathodes of the electronic elements I3 and with a biasing network I8, comprising a battery 25, or other source ofA biasing potential, and a resistor 21 for each electronic valve I3. The resistors 21 and battery 25 are preferably arranged in shunt relationship and each resistor has an associated adjustable slide contactor 29, whereby the same is The plate of each valve I3 is connected through a coupling condenser 3| to one end of the primary winding of the output vtransformer I'I. Each plate is also connected through a resistor 33 to a battery 35, or other suitable source of plate current. The battery is also connected to the cathodes of both valves I3.

The secondary winding of the output transformer may be connected to any desired network, in which it is desired to deliver the impulses from the equalizer system.

My equalizer system is especially well adapted for use in the receiving circuit of a radio or other transmission system, in which transmission is to be accomplished by means of a carrier wave of predetermined uniform frequency, transmitted at intervals in the form of coded impulse sets, and at the receiver delivered through the signal equalizer and then to filtering and amplifying circuits and decoding means, whereby the impulse sets may be separated and applied in the performance of individualv functions, for instance, the operation of a character printer forming a part of an automatic typewriter.

Ina particular application of my present invention, I utilize the signal equalizer system to actuate a system including a relay I9, in such a way that the relay is only caused to operate in response to the impression of a Wave of predetermined frequency upon the input II. The relay I9, however, is actuated from the output transformer I'I through an electrical network preferably including a sensitive actuating system 22, a lter 2 and, if desired, an amplier 26. The actuating system 22 preferably includes an electronic relay 28, such as a Thyratron, or other gas filled arc like discharge tubes, the plate circuit of which includes the actuating element or coil of the relay I9 and a source of plate current 3i'. The grid c ircuit is or may be pivoted with suitable adjustable biasing means 32. Impulses are delivered to the input of the relay actuating system 22 from the output transformer Il, through a lter 24 designed to pass the impulses having only a desired operating frequency.

Since the equalizer system, as previously mentioned, reduces all impulses applied at the input Ii to a common, constant amplitude, it is obvious that the filter 26 may be constructed in a most efficient manner having a capacity only sufficient to exclude interfering impulses of undesired frequency at the amplitude to which the same have been reduced in passing the equalizer systerm Consequently, I am able, with an inexpensive lter, to positively exclude from the actuating system 22 all but impulses having a desired frequency characteristic. The Thyratron relay 28 also is of a character extremely sensitive to grid voltages above the critical value required to place the plate circuit, and hence the relay I9, in operation. By proper adjustment of the grid biasing means, I am able to cause the plate circuit to operate only in response to the application of a denite or desired maximum voltage on the input of the relay 28.Y Thus the relay I9 will operate only when the filter passes operating impulses of predetermined frequency and amplitude received from the equalizer. The lter does not pass impulses having higher than the desired maximum operating voltage, for the equalizer system delivers only impulses having a iiform maximum amplitude, so that the relay may never operate falsely in response to interfering impulses of excessive voltage.

While the bias-adjusting means 32 may be made adjustable to determine the strength of signals required to operate `the system 22, I prefer to maintain a xed bias upon the grid of the element 28 :and to utilize kthe amplier 26 'to adjust the strength of the impulses, received from the output of the equalizer 9, to a desired value. To this end, one side of the secondary of the transformer I1 is shown connected to the grid of a valve 20, forming a part of the amplifying system, through Volume adjusting means 36. The cathode of the valve 20 is connected through a .resistor-condenser network 39 for maintaining a desired operating bias on the grid of the valve. The plate and cathode of the valve 20 are also connected through a circuit including the .net- Work39, the battery 4I, or other source of plate current, to the output terminals to which the filter 24 or other network may be connected.

The relay I9, of course, may be utilized to perform any desired operative or control function, as, for example, a type-printing element.

In an actual set up of the system, which I have successfully used, the resistors 21 and 33 were given a value of 100,000 ohms; the thermionic values I3 and 20 were type No. 56 Radiotrons; the transformers I1 and 2| had a primary-secondary ratio of 1 to l; the coupling condensers 3I were given a capacity value of 0.01 microfarad; the resistor and condenser of the networks 39 were given values of 2,000 ohms resistance and 0.01 microfarad capacity respectively; the control potentiometer 36 has a resistance of 250,000 ohms; the grid potential control means 34 had a resistance of 100,000 ohms; while the electrical sources 25, 30, 32, 35, and 4I were given approximate potentials of 45 volts, 110 volts, 45 volts, 135 volts, and 135 volts respectively, and the element 28 was a type No. 885 Thyratron The curves 45 and 41 in Figure respectively depict grid voltage-plate current characteristics of the valves I3. The numeral 23 depicts an impressed signal wave, which is shown graphically, applied lin proper relative position in association with the graph of both curves 45 and 41, since the impressed Wave is applied to both of the valves I3. As heretofore stated, the grid of one of the valves I3 is biased relatively more negative, as indicated by the bias potential line 46 than is the other valve, the negative bias of which is indicated by the bias potential line 4B. The numerals 5I and 53, respectively, indicate the maximum ampltitude of grid potential produced as a result of the impression of the wave 23 on each of the valves. The point, at which these lines intersect the curves 45 and 41, in turn indicates the maximum amplitude of the resulting plate or anode current produced in each valve as a result of the impression of the wave 23 and it will be seen that, due to the dilerence in the bias potentials 46 and 48, the amplitude of plate current owing in one Valve is considerably larger than that caused to 110W in the other as indicated by the relative position of the plate current lines 52 and 54. The curves 55 and 51 depict ideal plate current curves produced respectively in the several valves. The currents represented by the curves 55 and 51 are, as heretofore mentioned, delivered in opposition to the primary winding of the output transformer I1, so that the resultant current in the secondary of said transformer as shown at 59 will be the difference between the currents illustrated by the curves 55 and 51. This diiference will always be a constant factor as long as the amplitude lines 5I and 53 of the impressed wave intersects the curves 45 and 41 in their straight portions. It is my purpose to operate the system in such fashion that the amplitude lines 5I and 53 at all times intersect the curves 45 and 41 in their straight portions, the system becoming inoperative when such a condition is not maintained. This, of course, will be determined for many signel impulses by the amount of bias applied to the valve to which the graph 45 relates. If the signal 23 is so weak that its maximum amplitude line 5I intersects the graph 45 at or below its curved portion, it is simply necessary to decrease the bias upon said valve in order to bring the amplitude line 5I within the straight portion of the graph 45. In such a case, of course, it may be necessary to alter the bias maintained upon the other valve in order to maintain a desired differential between the plate currents 55 and 51.

The characteristic graph lines 45 and 41 also may curve at their upper ends as indicated by the dotted extensions. The exact shape and relative position of such curvature will, of course, depend upon the particular valves employed. If the impressed signal 23, however, is so strong that its maximum aplitude line 53 intersects the graph 41 in its upper curved portion, it is simply necessary to increase the bias on said Valve to bring the amplitude line within the straight portion of the graph. In such case, also, it may be necessary to alter the bias potential on the other Valve to maintain a desired differential between the plate currents 55 and 51.

I prefer, however, to fix the bias potentials permanently and to adjust the signal by controlling its strength as by passing the same through suitable adjustable amplifier in advance of the equalizing system. In this fashion, the signal may be instantly brought within the operating range of the equalizer system without disturbing the bias potentials 46 and 48.

In Figure 2, which represents graphically the results of operating and testing a device embodying the invention, the lines 5I and 53 represent a two-volt signal wave 23 impressed upon the valves I3. The bias line 46 represents a. negative bias of 1l Volts, while the bias line 48 represents a negative bias of 9 volts. In such an arrangement, signals, varying in strength between a minimum value of two volts, represented by the line 5I, and a maximum Value determined only by the length of the straight portion of the graphs 45 and 41 (it being understood that the graphs, at their upper ends, will flatten out as indicated in dotted lines, the exact form ci" the curves being determined by the character of the valves employed), may be impressed upon the grids of the valves simultaneously, and the resultant of the output transformer I1 to the amplifying circuit, will comprise a current wave of constant amplitude iluctuating at the frequency of the impressed wave 23.

While in Figure 2, I have shown characteristic graphs 45 and 48 for valves having identical characteristics, I do not necessarily have to employ identical valves. On the contrary, the valves may be such that the curve of one is displaced in either direction along the axis of grid potential. For example, if the characteristic curve 45 for one valve occupies a position as shown in dotted lines at 45I, it will be necessary to maintain a bias of 13 volts negative, with a bias of 9 volts negative on the other valve, in order to maintain the differential in plate current illustrated by the curve 59. On the other hand, if the characteristic line 45 of the valve occurs in a relative position on the graph, as shown in dotted lines at i552, it will be necessary to maintain the same negative bias potential on both valves, to-Wit, in the example specified, a negative bias potential of 9 volts. 'Ihe invention, in other words, contemplates a system wherein the valves are so biased that, when the system is functioning, the current 59 delivered at the output and the corresponding voltage comprises a wave having constant amplitude, for the purpose of operating the sensitive device 28 in the manner heretofore described.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent is as follows:

l. In an electric circuit, the combination of a pair of electronic tubes, input and output circuits, the output circuits being connected in opposition, and means for maintaining a constant differential between the amplitudes of the pulsations in the output circuits resulting from pulsations imressed upon the input circuits.

2. In an electric circuit, the combination of a pair of electronic tubes, input and output circuits, the output circuits being connected in opposition, and means in the input circuits for maintaining a constant differential between the amplitudes of the pulsations in the output circuits resulting from pulsations impressed upon the input circuits.

3. In an electric circuit, the combination of a pair of electronic tubes, input circuits for said tubes for receiving impulses of varying ampltiude and impressing the same equally upon the respective tubes, a differential output 'circuit for said tubes, and means in thhe input circuit for Ymaintaining constant the amplitude of the resulting impulses in the differential output circuit.

4. An electrical control method which consists in transforming a plurality of electrical impulses of varying amplitudes and frequencies into impulses'of a common, constant amplitude butof varying frequencies, ltering out the impulses of other than a predetermined frequency range and impressing the resultant impulses of 'constant amplitude within said predetermined frequency range on a device to be controlled.

5. An electrical control method which consists in transforming a plurality of electrical impulses of varying amplitudes and frequencies into impulses of a common, constant amplitude but of varying frequencies, filtering out the impulses of other than a predetermined frequency range, amplifying resultant impulses of constant amplitude within said predetermined frequency range and applying the amplified impulses upon a device to be controlled.

6. An electrical control method which consists in transforming a plurality of electrical impulses of varying amplitudes and frequencies into impulses of a common, constant amplitude but of varying frequencies, amplifying said impulses, and then filtering out the impulses of other than Va predetermined frequency range, and impressing the resultant impulses of constant amplitude within said predetermined frequency range upon a device to be controlled.

7. An electrical signaling method Which consists of simultaneously amplifying, at predetermined rates which differ by a constant amount, electrical impulses of varying amplitudes, subtractively combining the amplified impulses to produce resultant impulses of a common, constant amplitude and then utilizing the resultant impulses to operate an electric signal.

8. An electrical signaling method which consists in simultaneously amplifying at predetermined rates which differ by a constant-amount electrical impulses having varying amplitudes and frequencies, subtractively combining the amplified impulses to produce resultant impulses of a common, constant amplitude but of varying frequencies, filtering the resultant impulses to eliminate impulses of all frequencies other than a predetermined desired frequency, and then utilizing the resulting impulses of constant amplitude and predetermined frequency to operate an electric signal.

9. In a signal system, or the like, a pair of electronic tubes having input and output circuits, a source of signal voltages, means for impressing upon the input circuits impulses derived from said signal voltages, an impedance, means for differentially connecting the output circuits to said impedance, and means in the input circuits for maintaining constant the amplitude of the voltages impressed across said impedance in response to signal voltages of varying amplitudes.

l0. In a signal system or the like, a pair of electronic tubes having input and output circuits, a source of signal voltages, means for Vimpressing upcn the input circuits impulses derived from said signal voltages, an impedance, means for differentially connecting the output circuits tosaid impedance, and means in the input circuits for maintaining constant the amplitudes of the voltages impressed across said impedance in response to signal voltages of varyingV amplitudes, and an amplifier operatively connected in the system for maintaining said voltage of constant amplitude above a predetermined amplitude.

' 1l. In an amplifier, the combination of a pair of thermionic tubes having input and output circuits, a source of signal voltages, means for connecting the input circuits in parallel to the source of signal voltages, an impedance, means for connecting the output circuits through said impedance in phase opposition, and adjustable means in the input circuits for maintaining the resultant impulses supplied to said impedance at an amplitude which is constantrand substantially independent of the amplitude of the signal voltages impressed on the input circuits.

l2. In a relay circuit, or the like, wherein impulses of varying amplitudes and frequencies are received thereby, the combination of an amplifier comprising a pair of electrionic tubes having input and output circuits, means for impressing the received impulses in parallel upon the input circuits of the tubes, means for connectingY the output circuits in opposition, and separate biasing means in the input circuit of each tube for maintaining a constant diiference of amplitude between the amplified impulses appearing in the output circuit of each tube.

13. In an amplier having an input and an output circuit, means for maintaining substantially constant the amplitude of the pulsations in the output circuit resulting from pukations irnpressed upon the input circuit comprising a pair of electronic tubes, circuit elements connecting the input terminals of said tubes in parallel across an input circuit, an output circuit to which said tubes are coupled in phase opposing relationship, and means impressed upon the respective tubes energizing voltages of such different and related magnitudes that both tubes operate upon linear portions of their respective characteristic curves whereby the amplitude of the impulses in the output circuit resulting from pulsations impressed upon the input circuit is maintained constant.

14. In a signal equalizer system, the combination of a pair of electronic tubes having each a grid, a cathode, and an anode, a source of impulses, a circuit for connecting the grid and cathode of one tube to said source of impulses, a circuit fcr connecting the grid and cathode of the other tube to said source of impulses in parallel.

to the grid and cathode of the rst tube, a load device, means for connecting the output terminals of the tubes to said load in opposition, biasing means connected in each of the grid-cathode circuits of such predetermined relative values that both electronic tubes operate upon different linear portions of their characteristic curves, whereby the amplitude of the resultant impulses supplied to the load device in response to impulses impressed upon the grid tubes is maintained constant.

l5. In a relay circuit, or the like, the combination of a relay, a gas filled discharge tube, having a critical operating Voltage, for controlling the relay, a pair of electronic tubes having input and output circuits for supplying operating voltages to the discharge tube, means for connecting the input circuits of the electronic tubes in parallel across a source of supply, means for connecting the output circuits of the electronic tubes to the input of the discharge tube in opposition, and means in the input circuits of the electronic tubes for maintaining a constant differential between the amplitudes of the impulses supplied by the output circuits of each tube to the input of the discharge tube, said constant diierential being greater in amount than the critical value of voltage required for the operation of the discharge tube.

16. In a relay circuit or the like, the combination of a relay, a gas lled discharge tube having a critical operating voltage, for controlling the relay, a pair of electronic tubes having input and output circuits for supplying operating voltages t0 the f ischarge tube, means for connecting the input circuits of the electronic tubes in parallel across a source of supply, means for connecting the output circuits of the electronic tubes to the input of the discharge tube, in opposition, and means in the input circuits of the electronic tubes for maintaining a constant differential between the amplitudes of the impulses supplied by the f output circuits of each tube to the input of the discharge tube, said constant differential being greater in amount than the critical value of voltage required for the operation of the discharge tube, said source of supply being adapted to imf press impulses of a'plurality of frequencies upon the input circuits of the electronic tubes, and the means for connecting the output circuits of the electronic tubes to the discharge tube comprising means for ltering out all impulses of other than the desired frequency appearing in the output circuits of the electronic tubes.

ARTHUR H. BUCKLEY. 

